Use of ex vivo and in vitro model of human respiratory tract to study the tropism, replication competence and pathogenesis of influenza B virus

Abstract

Despite causing regular seasonal epidemics worldwide and resulting in substantial hospitalization and death, study on influenza B virus (IBV) is still lacking. As evidence on the severity and prevalence of IBV infections increases, it is essential to have more thorough study on IBV. Our group used human ex-vivo respiratory explant cultures and in-vitro primary respiratory epithelial cells to investigate the tropism and pathogenesis of different IBV strains from year 1940 to 2012 of both Yamagata and Victoria lineages. The panel of IBVs and human seasonal IAVs were used to infect human bronchus and lung explants as well as primary human well-differentiated bronchial epithelial cells (dHBECs) and alveolar epithelial cells (pneumocytes). The explants and cells were prepared and isolated from residual tissues of patients underwent lung resection with approval from the Institutional Review Board of the University of Hong Kong and Hospital Authority, Hong Kong West Cluster. Viral replication kinetics and tropism were assessed using TCID50 and IHC assays. Host innate immune response at mRNA and protein levels was investigated using RT-qPCR and BD Cytometric Bead Array. Results showed that human bronchus and lung explants, dHBECs, and pneumocytes, all supported most IBV replication with stronger tropism for the conducting airway than lung. Interestingly, IBVs induced earlier pro-inflammatory cytokine and chemokine expression in infected dHBECs and pneumocytes compared to IAVs. Significantly more IFNβ, IL29, CCL5, CXCL10, TNFα, MX1, and ISG15 mRNA were also induced in IBV-than IAV-infected dHBECs at 24 hours post infection. These results highlighted the non-negligible virulence of IBVs which requires more investigation to alleviate the disease burden.